Contribution distinguish between emission reduction and meteorological conditions to “Blue Sky”

Abstract Emissions and meteorological conditions are two important factors on aerosol accumulation or dilution. Identifying the contributions of both emission reduction (ER) and meteorological conditions (MC) on aerosol pollution abatement is a hot topic recently. An objective assessment of ER measures' contribution on improving air quality is also of great significance. This study focuses on objective assessment for the air quality improvements (known as “Blue Sky”) due to ER measures. A quantitative algorithm on identifying the contribution of ER measures was proposed. The emission-reducing contributions to the “Beijing blue” (August 20 to September 3, 2015, Beijing, International Association of Athletics Federations World Athletics Championships), the “Asia Pacific Economic Cooperation (APEC) blue” (November 10–11, 2014, Beijing, APEC meeting), and the “Games blue” (November 12–27, 2010, Guangzhou, 16th Asian Games) were studied based on pollutant MC of Parameters Linking Air-quality to Meteorological Conditions index. Two individual evaluation algorithms of an average change rate algorithm and a parameter fitting method were developed in this study. Results showed that the special comprehensive emission-reducing measures contributions were up to 26%–30% for “Beijing blue.” By analyzing the circulation anomaly during the “Beijing blue” with 30-year average historical atmospheric circulation and the real-time information in 3rd September 2015, we concluded that the “North China Cold Vortex,” as unusual stable circulation system stagnation, provides favorable weather conditions for the “Beijing blue.” This finding indicates that approximately 70%–74% of the “Beijing blue” came from long terms of favorable weather conditions. This algorithm for evaluating the contributions of ER and MC was also applied for the “APEC blue” and the “Games blue.” The contribution of emission-reducing measures on the “APEC blue” and the “Games blue” accounted for 36% and 25%, respectively. In summary, the favorable MC would contribute 65%–75% to the “Blue Sky” in China and acts as a remarkable role on the improvement of air quality.